32,377 research outputs found
The blue compact dwarf galaxy I Zw 18: a comparative study of its low-surface-brightness component
(abridged): Using HST and ground-based optical and NIR imaging data, we
investigate whether the blue compact dwarf (BCD) galaxy I Zw 18 possesses an
extended low-surface-brightness (LSB) old stellar population underlying its
star-forming (SF) regions. We show that the exponential intensity decrease
observed in the filamentary LSB envelope of the BCD out to 18 arcsec (1.3 kpc
at a distance of 15 Mpc) is not due to an evolved stellar disc, but rather due
to extended ionized gas emission. Broad-band images reveal, after subtraction
of nebular line emission, a compact stellar LSB component extending slightly
beyond the SF regions. This stellar host, being blue over a radius range of 5
exponential scale lengths and showing little colour contrast to the SF
component, differs strikingly from the red LSB host of standard BCDs. This
fact, in connection with the blue colors of component I Zw 18 C, suggests that
most of the stellar mass in I Zw 18 has formed within the last 0.5 Gyr.
Furthermore, we show that the exponential intensity fall-off in the filamentary
ionized envelope of I Zw 18 is not particular to this system but a common
property of the ionized halo of many SF dwarf galaxies on galactocentric
distances of several kpc. In the absence of an appreciable underlying stellar
background, extended ionized gas emission dominates in the periphery of I Zw
18, mimicking an exponential stellar disc on optical surface brightness
profiles.Comment: 24 pages, 16 figures; accepted for publication in Astronomy &
Astrophysics; higher resolution images available at
http://alpha.uni-sw.gwdg.de/~papade/IZw18
Structure in Supersymmetric Yang-Mills Theory
We show that requiring sixteen supersymmetries in quantum mechanical gauge
theory implies the existence of a web of constrained interactions. Contrary to
conventional wisdom, these constraints extend to arbitrary orders in the
momentum expansion.Comment: 22 pages, LaTe
Provenance for SPARQL queries
Determining trust of data available in the Semantic Web is fundamental for
applications and users, in particular for linked open data obtained from SPARQL
endpoints. There exist several proposals in the literature to annotate SPARQL
query results with values from abstract models, adapting the seminal works on
provenance for annotated relational databases. We provide an approach capable
of providing provenance information for a large and significant fragment of
SPARQL 1.1, including for the first time the major non-monotonic constructs
under multiset semantics. The approach is based on the translation of SPARQL
into relational queries over annotated relations with values of the most
general m-semiring, and in this way also refuting a claim in the literature
that the OPTIONAL construct of SPARQL cannot be captured appropriately with the
known abstract models.Comment: 22 pages, extended version of the ISWC 2012 paper including proof
Supersymmetric Wilson Loops in IIB Matrix Model
We show that the supersymmetric Wilson loops in IIB matrix model give a
transition operator from reduced supersymmetric Yang-Mills theory to
supersymmetric space-time theory. In comparison with Green-Schwarz superstring
we identify the supersymmetric Wilson loops with the asymptotic states of IIB
superstring. It is pointed out that the supersymmetry transformation law of the
Wilson loops is the inverse of that for the vertex operators of massless modes
in the U(N) open superstring with Dirichlet boundary condition.Comment: 10 pages, Latex, minor typos correcte
Non-renormalization conditions for four-gluon scattering in supersymmetric string and field theory
The constraints imposed by maximal supersymmetry on multi-loop contributions
to the scattering of four open superstrings in the U(N) theory are examined by
use of the pure spinor formalism. The double-trace term k^2 t_8(tr F^2)^2
(where k represents an external momentum and F the Yang--Mills field strength)
only receives contributions from L<=2 (where L is the loop number) while the
single-trace term k^2 t_8(tr F^4) receives contributions from all L. We
verified these statements up to L=5, but arguments based on supersymmetry
suggest they extend to all L. This explains why the single-trace contributions
to low energy maximally supersymmetric Yang--Mills field theory are more
divergent in the ultraviolet than the double-trace contributions. We also
comment further on the constraints on closed string amplitudes and their
implications for ultraviolet divergences in N=8 supergravity.Comment: 25 pages. 2 eps figures. Harvmac format. v2 qualifications regarding
comments on closed strings. References adde
Radio Observations of the Supernova Remnant Candidate G312.5-3.0
The radio images from the Parkes-MIT-NRAO (PMN) Southern Sky Survey at 4850
MHz have revealed a number of previously unknown radio sources. One such
source, G312.5-3.0 (PMN J1421-6415), has been observed using the
multi-frequency capabilities of the Australia Telescope Compact Array (ATCA) at
frequencies of 1380 MHz and 2378 MHz. Further observations of the source were
made using the Molonglo Observatory Synthesis Telescope (MOST) at a frequency
of 843 MHz. The source has an angular size of 18 arcmin and has a distinct
shell structure. We present the reduced multi-frequency observations of this
source and provide a brief argument for its possible identification as a
supernova remnant.Comment: 5 pages, 5 figures, Accepted for publication in MNRA
Coulomb screening in mesoscopic noise: a kinetic approach
Coulomb screening, together with degeneracy, is characteristic of the
metallic electron gas. While there is little trace of its effects in transport
and noise in the bulk, at mesoscopic scales the electronic fluctuations start
to show appreciable Coulomb correlations. Within a strictly standard Boltzmann
and Fermi-liquid framework, we analyze these phenomena and their relation to
the mesoscopic fluctuation-dissipation theorem, which we prove. We identify two
distinct screening mechanisms for mesoscopic fluctuations. One is the
self-consistent response of the contact potential in a non-uniform system. The
other couples to scattering, and is an exclusively non-equilibrium process.
Contact-potential effects renormalize all thermal fluctuations, at all scales.
Collisional effects are relatively short-ranged and modify non-equilibrium
noise. We discuss ways to detect these differences experimentally.Comment: Source: REVTEX. 16 pp.; 7 Postscript figs. Accepted for publication
in J. Phys.: Cond. Ma
Nonequilibrium mesoscopic transport: a genealogy
Models of nonequilibrium quantum transport underpin all modern electronic
devices, from the largest scales to the smallest. Past simplifications such as
coarse graining and bulk self-averaging served well to understand electronic
materials. Such particular notions become inapplicable at mesoscopic
dimensions, edging towards the truly quantum regime. Nevertheless a unifying
thread continues to run through transport physics, animating the design of
small-scale electronic technology: microscopic conservation and nonequilibrium
dissipation. These fundamentals are inherent in quantum transport and gain even
greater and more explicit experimental meaning in the passage to atomic-sized
devices. We review their genesis, their theoretical context, and their
governing role in the electronic response of meso- and nanoscopic systems.Comment: 21p
Views of patients about sickle cell disease management in primary care: a questionnaire-based pilot study.
OBJECTIVES: To determine how patients with sickle cell disease (SCD) perceive the quality of care that they receive from their primary healthcare providers. DESIGN: A questionnaire-based pilot study was used to elicit the views of patients about the quality of care they have been receiving from their primary healthcare providers and what they thought was the role of primary care in SCD management. SETTING: Sickle Cell Society and Sickle Cell and Thalassaemia Centre, in the London Borough of Brent. PARTICIPANTS: One hundred questionnaires were distributed to potential participants with SCD between November 2010 and July 2011 of which 40 participants responded. MAIN OUTCOME MEASURES: Analysis of 40 patient questionnaires collected over a nine-month period. RESULTS: Most patients are generally not satisfied with the quality of care that they are receiving from their primary healthcare providers for SCD. Most do not make use of general practitioner (GP) services for management of their SCD. Collecting prescriptions was the reason most cited for visiting the GP. CONCLUSION: GPs could help improve the day-to-day management of patients with SCD. This could be facilitated by local quality improvement schemes in areas with high disease prevalence. The results of the survey have been used to help develop a GP education intervention and a local enhanced service to support primary healthcare clinicians with SCDs ongoing management
Higher Derivative Corrections to Eleven Dimensional Supergravity via Local Supersymmetry
In this paper we derive higher derivative corrections to the eleven
dimensional supergravity by applying the Noether method with respect to the N=1
local supersymmetry. An ansatz for the higher derivative effective action,
which includes quartic terms of the Riemann tensor, is parametrized by 132
parameters. Then we show that by the requirement of the local supersymmetry,
the higher derivative effective action is essentially described by two
parameters. The bosonic parts of these two superinvariants completely match
with the known results obtained by the perturbative calculations in the type
IIA superstring theory. Since the calculations are long and systematic, we
build the computer programming to check the cancellation of the variations
under the local supersymmetry. This is an extended version of our previous
paper hep-th/0508204.Comment: 67 pages, no figure, references added, typos correcte
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